Welcome to HNet. If you want a black interior, then do it. General Lee replicas are thin on the ground here in Ireland, and the only one I've ever sat in (a couple of pictures here) had a black interior. I asked the owner about it, and he said he prefered it that way. A few owners try to get every detail right for a particular season, e.g. pushbar size, crossed flags decal, exact model of CB radio etc., but take a look at the parade of General Lees (below) and you'll see variations in color, different wheels and various other differences. Most are made to look like 1969 Chargers, but there are some 1968 and 1970 models in there too. My advice is to go with what you want.
BTW, don't forget to post pictures of your build .